The /device-node based configuration consists of a 16bit-value. A single nibble controls a specific 
part of the configuration, so it's easy to calculate the 16bit-word without paper+pencil.

These are the single nibbles:
	0x3210
	  ||||
	  |||+-- CHANNEL
	  ||+--- RESOLUTION / CONFIG
	  |+---- POWERSAVE / AVERAGING
	  +----- STATUS

CHANNEL: select ADC-channel
	BIT-NR	3210
		xx||
		  |+---- 0x0001 CH_SELECT0
		  +----- 0x0002 CH_SELECT1

	BIT-NR	1 0 | CHANNEL
	------------+--------
		0 0 | channel 0 (default)
		0 1 | channel 1
		1 0 | channel 2 (not available on gnublin board)
		1 1 | channel 3

RESOLUTION / CONFIG: select resolution (4bit, 8bit, 10bit), other configuration
	BIT-NR  3210
		|x||
		| |+---- 0x0010 RES_SELECT0
		| +----- 0x0020 RES_SELECT1
                |
		+------- 0x0080 DEBUG (if set, the driver will be verbose)

	BIT-NR	1 0 | Resolution
	------------+-----------
		0 0 | 10bit (default)
		0 1 | 8bit
		1 0 | 4bit

POWERSAVE / AVERAGING :
	BIT-NR	3210
		||||
		|||+---- 0x0100 POWERSAVE_SELECT0
		||+----- 0x0200 POWERSAVE_SELECT1
		|+------ 0x0400 AVERAGING_MODE0
		+------- 0x0800 AVERAGING_MODE1

	BIT 	1 0 | Powersave Mode
	------------+--------
		0 0 | powersaving off, adc always on
		0 1 | auto on/off for adc, only on when needed, takes more time, saves power (default)
		1 0 | adc always off, results are always waste

	BIT 	3 2 | Averaging Mode
	------------+---------------
		0 0 | averaging off, single shot ad conversion
		0 1 | averaging on, build average from 10 conversions
		1 0 | averaging on, build average from 75 conversions
		1 1 | averaging on, build average from 150 conversions



STATUS: if any of these 4 bits is set, the driver will print it's status via printk to "dmesg".
all other configuration bits are DON'T CARE in this case, no operation/configuration
will be performed.